U.S. patent number 8,462,411 [Application Number 13/130,150] was granted by the patent office on 2013-06-11 for optical reflection element with drive and monitor elements separated by a separation groove.
This patent grant is currently assigned to Panasonic Corporation. The grantee listed for this patent is Kiyomi Furukawa, Soichiro Hiraoka, Shinsuke Nakazono, Jirou Terada. Invention is credited to Shigeo Furukawa, Soichiro Hiraoka, Shinsuke Nakazono, Jirou Terada.
United States Patent |
8,462,411 |
Hiraoka , et al. |
June 11, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Optical reflection element with drive and monitor elements
separated by a separation groove
Abstract
An optical reflection element includes a mirror portion and an
oscillator coupled to the mirror portion. The oscillator includes a
base, an insulating layer, a drive element, and a monitor element.
The insulating layer is formed on the base. The drive element and
the monitor element are formed on the insulating layer, and are
separated from each other by a separation groove. Each of the drive
element and the monitor element includes a lower electrode layer, a
piezoelectric layer, and an upper electrode layer formed in that
order on the insulating layer. The monitor element has high
detection accuracy, allowing the optical reflection element to
perform self-excited driving with high accuracy.
Inventors: |
Hiraoka; Soichiro (Hyogo,
JP), Terada; Jirou (Osaka, JP), Nakazono;
Shinsuke (Osaka, JP), Furukawa; Shigeo (Osaka,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hiraoka; Soichiro
Terada; Jirou
Nakazono; Shinsuke
Furukawa; Kiyomi |
Hyogo
Osaka
Osaka
Osaka |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
42198008 |
Appl.
No.: |
13/130,150 |
Filed: |
November 18, 2009 |
PCT
Filed: |
November 18, 2009 |
PCT No.: |
PCT/JP2009/006190 |
371(c)(1),(2),(4) Date: |
June 20, 2011 |
PCT
Pub. No.: |
WO2010/058565 |
PCT
Pub. Date: |
May 27, 2010 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
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US 20110292479 A1 |
Dec 1, 2011 |
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Foreign Application Priority Data
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|
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Nov 20, 2008 [JP] |
|
|
2008-296354 |
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Current U.S.
Class: |
359/199.4;
310/311; 359/200.7 |
Current CPC
Class: |
G02B
26/0858 (20130101); G02B 26/101 (20130101) |
Current International
Class: |
G02B
26/08 (20060101); G02B 26/10 (20060101); G02B
26/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
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2006-293116 |
|
Oct 2006 |
|
JP |
|
2006-320089 |
|
Nov 2006 |
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JP |
|
2008-040240 |
|
Feb 2008 |
|
JP |
|
Other References
International Search Report for PCT/JP2009/006190, Dec. 5, 2009,
Panasonic Corp. cited by applicant .
Masanao Tani et al., "An Image Display Using Piezoelectric MEMS
Optical Scanner", Laser Review, Apr. 15, 2008, vol. 36, No. 4, pp.
183 to 189. cited by applicant.
|
Primary Examiner: Allen; Stephone
Assistant Examiner: Dabbi; Jyotsna
Attorney, Agent or Firm: RatnerPrestia
Claims
The invention claimed is:
1. An optical reflection element comprising: a mirror portion; and
an oscillator coupled to the mirror portion, the oscillator
comprising: a base; an insulating layer formed on the base; a drive
element and a monitor element formed on the insulating layer, the
drive element and the monitor element being separated from each
other by a separation groove, wherein each of the drive element and
the monitor element includes a lower electrode layer, a
piezoelectric layer, and an upper electrode layer formed in that
order on the insulating layer; the lower electrode layer of the
drive element and the lower electrode layer of the monitor element
are connected to a same external electrode layer; and a shortest
conductive path between an arbitrary point of the lower electrode
layer of the monitor element and an arbitrary point of the lower
electrode layer of the drive element adjacent to the monitor
element is made larger than a distance from the arbitrary point of
the lower electrode layer of the monitor element to the external
electrode layer by the separation groove.
2. The optical reflection element of claim 1, wherein the
separation groove between the drive element and the monitor element
has a bottom surface located inside the insulating layer.
3. The optical reflection element of claim 1, wherein the
separation groove between the drive element and the monitor element
has a bottom surface located inside the base.
4. The optical reflection element of claim 3, wherein the
separation groove is made deeper from an outer periphery thereof
toward a center thereof.
5. The optical reflection element of claim 3, wherein the
separation groove is made deeper from a center thereof toward an
outer periphery thereof.
6. The optical reflection element of claim 1, wherein a thickness
ratio of the insulating layer to the lower electrode layer is made
larger than an etching rate ratio of the insulating layer to the
lower electrode layer.
7. The optical reflection element of claim 1, wherein the
oscillator is formed in a meandering shape and includes oscillating
plates folded and coupled to each other on a same plane.
8. The optical reflection element of claim 2, wherein the
separation groove is made deeper from an outer periphery thereof
toward a center thereof.
9. The optical reflection element of claim 2, wherein the
separation groove is made deeper from a center thereof toward an
outer periphery thereof.
Description
This application is a U.S. National Phase Application of PCT
international application PCT/JP2009/006190.
TECHNICAL FIELD
The present invention relates to an optical reflection element used
in display and other devices.
BACKGROUND ART
FIG. 10 shows conventional optical reflection element 1. Optical
reflection element 1 includes mirror portion 2, a pair of first
oscillators 3 and 4, frame body 5, and a pair of second oscillators
6 and 7. First oscillators 3 and 4 are coupled to the ends of
mirror portion 2. Frame body 5 is coupled to first oscillators 3
and 4, and surrounds the outer peripheries of first oscillators 3,
4 and mirror portion 2. Second oscillators 6 and 7 are coupled to
the ends of frame body 5.
First oscillators 3 and 4 have an axis S1 as their central axis,
which is parallel to the y-axis. Second oscillators 6 and 7 have an
axis S2 as their central axis, which is parallel to the x-axis.
Thus, first oscillators 3, 4 and second oscillators 6, 7 are formed
in a meandering shape.
First oscillators 3, 4 and second oscillators 6, 7 include a drive
element. The drive element is composed of a lower electrode layer,
a piezoelectric layer, and an upper electrode layer. By applying
voltage to the drive element, mirror portion 2 rotates about axes
S1 and S2. Then, by applying light to mirror portion 2 while it is
rotating, the x-y surface of a screen can be scanned with reflected
light. As a result, an image can be projected onto a wall, a
screen, or the like.
First oscillators 3, 4, second oscillators 6, 7, and mirror portion
2 also include a monitor element. The monitor element is also
composed of a lower electrode layer, a piezoelectric layer, and an
upper electrode layer. The monitor element detects an electrical
signal, and supplies the signal to the upper electrode layer of the
drive element via a feedback circuit. As a result, in theory,
optical reflection element 1 can be driven constantly at the
resonant frequency, thereby having a large amplitude. Such optical
reflection elements are referred to as self-excited driving
type.
An example of a conventional technique related to the present
invention is shown in Patent Literature 1.
In this example, however, when the driving frequency is too high,
the optical reflection element sometimes cannot perform
self-excited driving.
The reason for this is considered as follows. Arranging a ground
electrode lengthwise increases the resistance. The increased
resistance causes current leakage between the upper electrode layer
of the monitor element and the upper electrode layer of the drive
element adjacent to the monitor element.
This decreases the detection accuracy of the monitor element,
making is impossible for the optical reflection element to perform
self-excited driving.
CITATION LIST
Patent Literature
Patent Literature 1: Japanese Patent Unexamined Publication No.
2008-040240
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical
reflection element having a monitor element with high detection
accuracy, thereby performing self-excited driving with high
accuracy.
The optical reflection element of the present invention includes a
mirror portion, and an oscillator coupled to the mirror portion.
The oscillator includes a base, an insulating layer, a drive
element, and a monitor element. The insulating layer is formed on
the base. The drive element and the monitor element are formed on
the insulating layer, and are separated from each other by a
separation groove. Each of the drive element and the monitor
element includes a lower electrode layer, a piezoelectric layer,
and an upper electrode layer formed in that order on the insulating
layer. The lower electrode layer of the drive element and the lower
electrode layer of the monitor element are connected to the same
external electrode. The separation groove allows the shortest
conductive path between an arbitrary point of the lower electrode
layer of the monitor element and an arbitrary point of the lower
electrode layer of the drive element adjacent to the monitor
element to be set to be longer than the distance from the arbitrary
point of the lower electrode layer of the monitor element to the
external electrode.
The optical reflection element of the present invention has a
monitor element with high detection accuracy, thereby performing
self-excited driving with high accuracy.
More specifically, the ground resistance of the lower electrode of
the monitor element can be made lower than the conductive
resistance between the lower electrode of the monitor element and
the lower electrode of the drive element.
This structure can prevent current leakage between the upper
electrode layer of the monitor element and the upper electrode
layer of the drive element even when the lower electrode layer is
arranged lengthwise.
As a result, the monitor element has high detection accuracy,
allowing the optical reflection element to perform self-excited
driving with high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an optical reflection element
according to a first exemplary embodiment of the present
invention.
FIG. 2A is a perspective view of first oscillators in the optical
reflection element according to the first exemplary embodiment.
FIG. 2B is a sectional view (taken along an axis S1 of FIG. 2A) of
the first oscillators in the optical reflection element according
to the first exemplary embodiment.
FIG. 3 is a sectional view (taken along an axis S2 of FIG. 1) of
one second oscillator in the optical reflection element according
to the first exemplary embodiment.
FIG. 4 is a sectional view (taken along the axis S2 of FIG. 1) of
the other second oscillator in the optical reflection element
according to the first exemplary embodiment.
FIG. 5 is a block diagram of a driving circuit for driving the
optical reflection element according to the first exemplary
embodiment.
FIG. 6 is a schematic diagram of the operation of first oscillators
in the optical reflection element according to the first exemplary
embodiment.
FIG. 7 is a sectional view of an essential part of another example
of the optical reflection element according to the first exemplary
embodiment.
FIG. 8 is a sectional view of an essential part of further another
example of the optical reflection element according to the first
exemplary embodiment.
FIG. 9 is a sectional view of an essential part of further another
example of the optical reflection element according to the first
exemplary embodiment.
FIG. 10 is a perspective view of a conventional optical reflection
element.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
First Exemplary Embodiment
The structure of an optical reflection element of the present
exemplary embodiment will be described as follows with reference to
FIGS. 1 to 4. FIG. 1 is a perspective view of the optical
reflection element. FIGS. 2A and 2B are a perspective view and a
sectional view, respectively, of first oscillators in the optical
reflection element. FIGS. 3 and 4 are sectional views of one second
oscillator and the other second oscillator, respectively, in the
optical reflection element.
In FIG. 1, optical reflection element 8 of the present exemplary
embodiment includes mirror portion 9 and a pair of first
oscillators 10 and 11. First oscillators 10 and 11 are opposed to
each other in the y-axis direction with mirror portion 9
therebetween, and are coupled to the ends of mirror portion 9.
Optical reflection element 8 further includes frame body 12. Frame
body 12 is coupled to first oscillators 10 and 11, and surrounds
the outer peripheries of first oscillators 10, 11 and mirror
portion 9. Optical reflection element 8 further includes a pair of
second oscillators 13 and 14, and frame-like support body 15.
Second oscillators 13 and 14 are opposed to each other in the
x-axis direction with frame body 12 therebetween, and are coupled
to frame body 12. Support body 15 is coupled to second oscillators
13 and 14, and surrounds the outer peripheries of second
oscillators 13, 14 and frame body 12. First oscillators 10 and 11
are arranged at right angles to second oscillators 13 and 14.
First oscillators 10 and 11 have a resonant driving frequency
different from second oscillators 13 and 14. The frequency
difference between them is about 10 to 100 times. In the present
exemplary embodiment, first oscillators 10 and 11 have a resonant
frequency of 10 kHz, and second oscillators 13 and 14 have a
resonant frequency of about 200 Hz.
The central axis S1 of first oscillators 10, 11 and the central
axis S2 of second oscillators 13, 14 cross each other. In the
present exemplary embodiment, these axes S1 and S2 cross at the
center of gravity of mirror portion 9. First oscillators 10 and 11
are symmetrical with respect to central axis S2 of second
oscillators 13 and 14. Second oscillators 13 and 14 are symmetrical
with respect to central axis S1 of first oscillators 10 and 11.
First oscillators 10 and 11 in the present exemplary embodiment
include oscillating plates 10A to 10D and 11A to 11D, and are
formed in a meandering shape. Oscillating plates 10A to 10D and 11A
to 11D are folded and coupled to each other in parallel with the
x-axis (perpendicular to the central axis S1) on the same plane.
Second oscillators 13 and 14 include oscillating plates 13A to 13E
and 14A to 14E, and are formed in a meandering shape. Oscillating
plates 13A to 13E and 14A to 14E are folded and coupled to each
other in parallel with the y-axis (perpendicular to the central
axis S2) on the same plane.
FIG. 2B is a sectional view of first oscillators taken along the
central axis S1. In FIG. 2B, oscillating plates 10A to 10D and 11A
to 11D composing first oscillators 10 and 11 include drive element
16 and monitor element 17 on their top portion.
FIG. 3 shows a sectional view of second oscillator 13 taken along
the central axis S2. In FIG. 3, oscillating plates 13A to 13E
composing second oscillator 13 include drive element 16 and monitor
element 17. Drive element 16 is shared among first and second
oscillators 10, 11, 13, and 14. Monitor element 17 detects the
oscillation of first oscillators 10 and 11.
FIG. 4 is a sectional view of second oscillator 14 taken along the
central axis S2. In FIG. 4, oscillating plates 14A to 14E composing
second oscillator 14 include drive element 16 and monitor element
18. Drive element 16 is shared among first and second oscillators
10, 11, 13, and 14. Monitor element 18 detects the oscillation of
second oscillator 14.
As shown in FIGS. 2B, 3, and 4, each of first oscillators 10, 11
and second oscillator 13 includes base 19, insulating layer 20,
drive element 16, and monitor element 17. Insulating layer 20 is
formed on base 19. Drive element 16 and monitor element 17 are
formed on insulating layer 20, and are separated from each other by
separation groove 30A. Second oscillator 14 includes base 19,
insulating layer 20, drive element 16, and monitor element 18.
Insulating layer 20 is formed on base 19. Drive element 16 and
monitor element 18 are formed on insulating layer 20, and are
separated from each other by separation groove 30A.
Drive element 16 includes lower electrode layer 21, piezoelectric
layer 22, and upper electrode layer 23 formed on insulating layer
20 in that order.
Similarly, monitor element 17 includes lower electrode layer 21,
piezoelectric layer 22, and upper electrode layer 24 formed on
insulating layer 20 in that order. Monitor element 18 includes
lower electrode layer 21, piezoelectric layer 22, and upper
electrode layer 25 formed on insulating layer 20 in that order.
In the present exemplary embodiment, in FIG. 1, upper electrode
layer 23 of drive element 16 at the top portion of each of first
oscillators 10, 11 and second oscillators 13, 14 is connected to
interconnect electrode 26 formed on support body 15. Upper
electrode layer 24 of monitor element 17 (see FIG. 2B) at the top
portion of each of first oscillators 10 and 11 is connected to
interconnect electrode 27 via upper electrode layer 24 of second
oscillator 13. Upper electrode layer 25 of monitor element 18 (see
FIG. 4) at the top portion of second oscillator 14 is connected to
interconnect electrode 28. Lower electrode layers 21 of drive
element 16 and of monitor elements 17 and 18 shown in FIGS. 2B, 3,
and 4 are connected to the same interconnect electrode 29 shown in
FIG. 1.
Support body 15 includes an external electrode layer (not
illustrated). The external electrode layer is connected to the
lower electrode layers of drive element 16 and of monitor elements
17, 18, and is also connected to interconnect electrode 29.
In FIGS. 2A, 2B, 3, and 4, drive element 16 and monitor element 17
or 18 are parallelly arranged adjacent to each other at the top
portion of each of oscillating plates 10A to 10D, 11A to 11D, 13A
to 13E, and 14A to 14E. More specifically, in each oscillating
plate, drive element 16 and monitor element 17 or 18 are arranged
on the same insulating layer 20 formed on the same base 19, and are
separated from each other by separation groove 30A.
Separation groove 30A reaches insulating layer 20 so that its
bottom surface is located inside insulating layer 20.
In the present exemplary embodiment, base 19 is made of a silicon
wafer, but may alternatively be made of, for example, a MgO or
stainless wafer.
Insulating layer 20 can be made of silicon dioxide. Lower electrode
layer 21 can be made of platinum. Upper electrode layers 23, 24,
and 25 can be made of gold. Piezoelectric layer 22 can be made of
lead zirconate titanate (Pb(Zr.sub.x,Ti.sub.1-x)O.sub.3 where
x=0.525). These materials can be formed into thin films by
deposition, sol-gel, CVD, sputtering, or other methods.
Separation groove 30A can be formed by patterning upper electrode
layers 23, 24, and 25 by dry etching, wet etching, or other
methods, and then by patterning piezoelectric layer 22, lower
electrode layer 21, and insulating layer 20 in that order by dry
etching. However, in the case that lower electrode layer 21 is made
of platinum and insulating layer 20 is made of silicon dioxide, it
is difficult to locate the bottom surface of separation groove 30A
inside insulating layer 20. This is because silicon dioxide is
etched at a higher rate than platinum. Therefore, the thickness
ratio of insulating layer 20 to lower electrode layer 21 is
preferably larger than the etching rate ratio of insulating layer
20 to lower electrode layer 21.
The following is a description, with reference to FIG. 5, of a
method for driving optical reflection element 8 of the present
exemplary embodiment. FIG. 5 is a block diagram of a driving
circuit for driving the optical reflection element.
In FIG. 5, the driving circuit includes amplifiers 31 and 32 which
are arranged in parallel to each other. Amplifier 31 receives and
amplifies an electrical signal (an AC voltage) for driving first
oscillators 10 and 11. Amplifier 32 receives and amplifies an
electrical signal (an AC voltage) for driving second oscillators 13
and 14.
The electrical signal received by first oscillators 10 and 11 has
an oscillation frequency unique to them, allowing first oscillators
10 and 11 to be driven resonantly. The electrical signal received
by second oscillators 13 and 14 has an oscillation frequency unique
to them, allowing second oscillators 13 and 14 to be driven
resonantly. As a result, first oscillators 10, 11 and second
oscillators 13, 14 can be driven constantly at the resonant
frequency. Thus, first oscillators 10, 11 and second oscillators
13, 14 are efficiently driven and largely displaced.
The electrical signals amplified by amplifiers 31 and 32 are
combined by impedance elements 33 and 34 such as resistors, and are
supplied to interconnect electrode 26.
The combined electrical signal is derived from interconnect
electrode 26 to upper electrode layer 23 which is shared among
first and second oscillators 10, 11, 13, and 14. This results in
driving drive element 16, thereby displacing first oscillators 10,
11 and second oscillators 13, 14.
Upper electrode layer 24 of monitor element 17 at the top portion
of each of first oscillators 10 and 11 detects the displacement of
first oscillators 10 and 11 as an electrical signal. This
electrical signal is derived by interconnect electrode 27 via upper
electrode layer 24 which is routed to second oscillator 13.
Similarly, upper electrode layer 25 of monitor element 18 at the
top portion of second oscillator 14 detects the displacement of
second oscillator 14 as an electrical signal. This electrical
signal is derived to interconnect electrode 28.
This electrical signal derived to interconnect electrode 27 is
taken through filter 35 and is supplied again to amplifier 31.
The electrical signal derived to interconnect electrode 28 is taken
through filter 36 and is supplied again to amplifier 32.
Thus, the electrical signals outputted from upper electrode layers
24 and 25 (monitor electrodes) of monitor elements 17 and 18,
respectively, are fed back to upper electrode layer 23 (a drive
electrode) of drive element 16 which is shared among first and
second oscillators 10, 11 13, and 14. As a result, optical
reflection element 8 can perform self-excited driving.
Impedance elements 33 and 34 can be reactive elements such as
capacitors, coils, or a combination of them, instead of
resistors.
In the present exemplary embodiment, drive element 16 shared among
first and second oscillators 10, 11, 13, and 14 includes a single
upper electrode layer 23 in order to apply the combined electrical
signal to upper electrode layer 23. In other words, upper electrode
layer 23 of drive element 16 is shared among first and second
oscillators 10, 11 13, and 14. Alternatively, however, optical
reflection element 8 can be driven by other circuitry. For example,
it is possible to provide two upper electrode layers 23
electrically independent of each other: one in first oscillators 10
and 11, and the other in second oscillators 13 and 14.
The following is a description of the operation of optical
reflection element 8 of the present exemplary embodiment.
In FIGS. 2A and 2B, drive element 16 is formed to have a large
width on every other oscillating plate between oscillating plates
10A to 10D of first oscillator 10 and between oscillating plates
11A to 11D of first oscillating plate 11. More specifically, drive
element 16 is formed to have a large width on oscillating plates
10B, 10D, 11B, and 11D. Assume that an AC voltage (an electrical
signal) at the resonant frequency of first oscillators 10 and 11 is
applied to upper electrode layer 23 of drive element 16. Then,
oscillating plates 10B, 10D, 11B, and 11D having drive element 16
with the large width on their top portion flexurally oscillate in
their thickness direction. Oscillating plates 10A, 10C, 11A, and
11C which are adjacent to oscillating plates 10B, 10D, 11B, and 11D
flexurally oscillate in the opposite direction according to the
principle of resonance. Thus, oscillating plates 10A to 10D and 11A
to 11D oscillate in such a manner that adjacent oscillating plates
are in opposite phases. Then, as shown in FIG. 6, displacement
accumulates at central axis S1, allowing mirror portion 9 to
repeatedly oscillate at a large amplitude about the central axis
S1. Drive element 16 is formed to have a small width on oscillating
plates 10A, 10C, 11A, and 11C which are adjacent to oscillating
plates 10B, 10D, 11B, and 11D having drive element 16 with the
large width on their top portion. Oscillating plates 10A, 10C, 11A,
and 11C, to which substantially no voltage is applied, are
displaced in the phase opposite to oscillating plates 10B, 10D,
11B, and 11D having drive element 16 with the large width on their
top portion.
In FIGS. 3 and 4, similar to first oscillators 10 and 11, drive
element 16 is formed to have a large width on every other
oscillating plate between oscillating plates 13A to 13E and 14A to
14E of second oscillators 13 and 14. Assume that an AC voltage at
the resonant frequency of second oscillators 13 and 14 is applied
to upper electrode layer 23 of drive element 16. Then, oscillating
plates 13A, 13C, 13E, 14A, 14C, and 14E having drive element 16
with the large width on their top portion flexurally oscillate in
their thickness direction. Oscillating plates 13B, 13D, 14B, and
14D which are adjacent to oscillating plates 13A, 13C, 13E, 14A,
14C, and 14E flexurally oscillate in the direction opposite to
oscillating plates 13A, 13C, 13E, 14A, 14C, and 14E according to
the principle of resonance. Thus, oscillating plates 13A to 13E and
14A to 14E oscillate in such a manner that adjacent oscillating
plates are in opposite phases. As a result, frame body 12 and
mirror portion 9 can repeatedly oscillate at a large amplitude
about central axis S2.
As described above, in the present exemplary embodiment, mirror
portion 9 can be rotated about its center in the directions of the
two axes S1 and S2.
In the present exemplary embodiment, in each of oscillating plates
10, 11, 13, and 14, drive element 16 and monitor element 17 or 18
are arranged adjacently and in parallel to each other. In each
oscillating plate, the shortest conductive path between an
arbitrary point of lower electrode layer 21 of monitor element 17
or 18 and an arbitrary point of lower electrode layer 21 of drive
element 16 adjacent to monitor element 17 or 18 is set to be longer
than the distance from the arbitrary point of lower electrode layer
21 of monitor element 17 or 18 to interconnect electrode 29. The
above-mentioned shortest conductive path in the present exemplary
embodiment means, for example, a path from lower electrode layer 21
of monitor element 17 or 18 to lower electrode layer 21 of drive
element 16 via deriving electrode 29. To achieve this structure, in
the present exemplary embodiment, the bottom surface of separation
groove 30A formed between drive element 16 and monitor element 17
or 18 at the top portion of each oscillating plate is located
inside insulating layer 20.
As a result, even when lower electrode layers 21 of monitor
elements 17 and 18 are arranged lengthwise, the ground resistance
of lower electrode layers 21 of monitor elements 17 and 18 can be
relatively lower than the conductive resistance between lower
electrode layers 21 of monitor elements 17, 18 and lower electrode
layer 21 of drive element 16.
This reduces leakage of an electrical signal from the upper
electrode of drive element 16 to upper electrode layers 24 and 25
of monitor elements 17 and 18, respectively, via lower electrode
layer 21 and piezoelectric layer 22 of each of drive element 16 and
monitor elements 17, 18 either between upper electrode layers 23
and 24 of drive element 16 and monitor element 17, respectively, or
between upper electrode layers 23 and 25 of drive element 16 and
monitor element 18, respectively.
Impedance due to capacitance decreases with increasing driving
frequency, thereby increasing current leakage, which is a problem
addressed by the present invention. Therefore, the structure of the
present exemplary embodiment is useful to increase the detection
accuracy of monitor element 17 of first oscillators 10 and 11 which
are driven at a high frequency.
In the present exemplary embodiment, both in first oscillators 10,
11 and in second oscillators 13, 14, the etching is performed until
the bottom surface of separation groove 30A reaches insulating
layer 20. This ensures separation between lower electrode layer 21
of drive element 16 and lower electrode layer 21 of monitor element
17 or 18, thereby preventing capacitive coupling or electrical
continuity between the residual portions of these lower electrode
layers 21. Thus, even when lower electrode layers 21 are arranged
lengthwise, it is possible to reduce current leakage between upper
electrode layers 23 and 24 of drive element 16 and monitor element
17, respectively, or between upper electrode layers 23 and 25 of
drive element 16 and monitor element 18, respectively. This
increases the detection accuracy of monitor elements 17 and 18,
allowing optical reflection element 8 to perform self-excited
driving with high accuracy.
In optical reflection element 8 requiring a large amplitude, first
oscillators 10, 11 and second oscillators 13, 14 may be formed in a
meandering shape as in the present exemplary embodiment. In this
case, the oscillators have very long beams. As a result, lower
electrode layers 21 are arranged lengthwise, thereby failing to be
sufficiently grounded. In the present exemplary embodiment,
however, even when lower electrode layers 21 are not sufficiently
grounded, it is possible to reduce current leakage between drive
element 16 and monitor element 17 or 18. As a result, optical
reflection element 8 of the present invention performs self-excited
driving with high accuracy.
Upper electrode layer 23 of monitor element 17 of first oscillators
10 and 11 is routed to second oscillators 13 and 14. As a result,
lower electrode layers 21 are arranged further lengthwise. Thus,
the structure of the present exemplary embodiment is useful to
realize high detection accuracy of monitor element 17 of first
oscillators 10 and 11.
In the present exemplary embodiment, the bottom surface of
separation groove 30A is formed of insulating layer 20. As a
result, even when a conductive component adheres to the bottom
surface, this does not result in electrical continuity. In
addition, even when a dielectric component adheres to the bottom
surface, this does not lead to capacitive coupling which causes
leakage.
In the present exemplary embodiment, insulating layer 20 is made of
silicon dioxide having a smaller dielectric constant than other
materials often used for piezoelectric layer 22. Therefore, even
when a conductive component adheres to the bottom surface of
separation groove 30A, for example, during etching, this does not
lead to capacitive coupling which causes leakage. In addition, even
when a dielectric component adheres to the bottom surface, this
does not cause noise. As a result, the detection accuracy of
monitor elements 17 and 18 is increased.
In the present exemplary embodiment, upper electrode layer 23,
which is the drive electrode of drive element 16 is shared among
first and second oscillators 10, 11, 13, and 14. This results in
the reduction of the number of wirings connected to of the
electrodes routed on optical reflection element 8. As a result,
production efficiency is increased, and electrical interference
between the electrodes is minimized.
Separation groove 30A is etched until its bottom surface is located
inside insulating layer 20 in the present exemplary embodiment, but
may alternatively be etched until its bottom surface is located
inside base 19 as shown in FIG. 7. In the latter case, the dense
surface of base 19 can be exposed so as to reduce adhesion of a
conductive or dielectric material to the surface, thereby further
reducing leakage.
Two electrical signals are combined by the impedance elements in
the present exemplary embodiment, but may alternatively be combined
by, for example, a preamplifier, a saturation amplifier, a
band-pass filter, and an additive combiner circuit. In the latter
case, the circuit is composed of active elements, allowing the
above-mentioned components to be incorporated into an IC chip,
thereby rationalizing the mounting process.
In first oscillators 10, 11 and second oscillators 13, 14, the use
of a single upper electrode layer allows oscillating plates 10A to
10D and 11A to 11D, and oscillating plates 13A to 13E and 14A to
14E to oscillate alternately in opposite phases according to the
principle of resonance. As a result, displacement accumulates,
thereby reducing the number of wirings connected to electrodes,
while maintaining a high oscillation efficiency.
The bottom surface of separation groove 30A is made flat in the
present exemplary embodiment. Alternatively, separation groove 30A
may be made deeper from the periphery toward the center as shown in
FIG. 8. This increases the insulation distance between lower
electrode layer 21 of drive element 16 and lower electrode layer 21
of monitor element 17, thereby reducing leakage. In addition, the
bottom surface in this case has a larger actual distance than the
flat bottom surface. This reduces leakage between upper electrode
layers 23 and 24 of drive element 16 and monitor element 17,
respectively, or between upper electrode layers 23 and 25 of drive
element 16 and monitor element 18, respectively, even when a
conductive or dielectric component adheres to separation groove
30A.
A similar effect can be obtained by making separation groove 30A
deeper from the center toward the periphery as shown in FIG. 9.
Separation groove 30A is formed in each of first oscillators 10,
and second oscillators 13, 14 in the present exemplary embodiment,
but may alternatively be formed only in first oscillators 10 and
11. The reason for this is as follows. First oscillators 10 and 11
are further from deriving electrode 29 than second oscillators 13
and 14 are. Therefore, first oscillators 10 and 11 are more likely
to cause current leakage than second oscillators 13 and 14. Forming
a separation groove at least in the first oscillators can prevent
current leakage, thereby increasing the detection accuracy of the
monitor element.
First oscillators 10, 11 and second oscillators 13, 14 are formed
in a meandering shape in the present exemplary embodiment, but may
alternatively be formed in a cantilever, a crisscross, or other
shapes. Optical reflection element 8 is operated in the two axial
directions by coupling first oscillators 10, 11 and second
oscillators 13, 14 to mirror portion 9 in the present exemplary
embodiment, but may alternatively be operated in a single axial
direction.
INDUSTRIAL APPLICABILITY
Optical reflection element 8 of the present invention is useful in
compact image projectors such as compact projectors, head-up
displays, and head-mounted displays.
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